Light-enhanced gating effect on the persistent photoconductivity at LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface

Abstract

The LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface has been one of the topics studied most during the past few years due to its many intriguing properties such as the two-dimensional electron gas, transient photoconductivity (PC), persistent photoconductivity (PPC), and the coexistence of the PC and PPC. Of them, the PPC effect is the most interesting because of its potential application in exploring the photoelectric memory devices. Until now, tuning of the PPC of the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface under the external stimuli, such as electric or magnetic field is less addressed, while the relevant knowledge is of great value for exploring the memory devices with multifunctionality. In this paper, we report on an electric field control of the persistent PPC at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface. Our LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterojunction is fabricated by growing the LaAlO<sub>3</sub> film on the SrTiO<sub>3</sub> substrates through using pulsed laser deposition. The substrate temperature is kept at 750 ℃ and the partial pressure of oxygen is maintained at 3.3 × 10<sup>–5</sup> Torr (1 Torr = 1.33322 × 10<sup>2</sup> Pa) during the deposition. The thickness of LaAlO<sub>3</sub> film is controlled to be about 2 nm by setting an appropriate deposition time. The X-ray diffraction experiment confirms that the LAO film is well epitaxial and of single phase. To guarantee the good electric contacts, Al electrodes are soldered at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface and the back side of the SrTiO<sub>3</sub> respectively by ultrasonic welding. We find that the PPC at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface can be significantly reinforced and modulated by the light-enhanced gating effects: that is, after a negative back gate voltage processing combined with a simultaneous light illumination, the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface can exhibit a notable PPC effect. And the PPC effect increases as the negative gate voltage increases, and then attains a maximum at a back gate voltage of about –70 V. Further increase of the negative gate voltage can cause the PPC to decrease. Additionally, the PPC is also found to increase monotonically with increasing the gating time. The present result can be understood in terms of the migration of the oxygen vacancies under the influence of photoelectric synergetic effect. This field enhanced PPC effects at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface may find their applications in designing the photoelectric memory devices with electric tunability.